docs: def previous(self):
          """Return the previous page.
  
          The page label is defined in ``settings.PREVIOUS_LABEL``.
          Return an empty string if current page is the first.
          """
          if self._page.has_previous():
              return self._endless_page(
                  self._page.previous_page_number(),
                  label=settings.PREVIOUS_LABEL)
          return ''